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Possible New Scrubber Material

Zeolitic imidazolate frameworks are metal-organic frameworkcarbon dioxide sinks which could be used to keep industrial emissions of carbon dioxide out of the atmosphere. One litre of the crystals could store about 83 litres of CO2. The crystals are non-toxic and require little energy to create, making them an attractive possibility for carbon capture and storage. "The porous structures can be heated to high temperatures without decomposing and can be boiled in water or solvents for a week and remain stable, making them suitable for use in hot, energy-producing environments like power plants."[1]

My question is how does 83 L/L compare to the soda lime based absorbent? Also this sounds like it could be safer than the current system.

Re: Possible New Scrubber Material

My question is how does 83 L/L compare to the soda lime based absorbent? Also this sounds like it could be safer than the current system.

Yes this could be very interesting. But I think we are a very long way from having anything suitable for our rebreathers.

The ordinary soda lime most of us use today has a practical capacity of roughly ~100-150 litres of CO2 per liter (depending on things like scrubber size, depth, water temp, how bold you are, etc.) The theroretical capacity on the other hand is more like 250+ litres of CO2 per liter.

I'm no expert but here are a few things I think could be problematic with reversible CO2 adsorption systems in rebreathers for diving:

Relying on more or less reversible adsorption rather than the practially "irreversible" absorbents such as soda lime introduces a few new tricks. The amount of CO2 that can be adsorbed could depend quite strongly on the partial pressure of CO2. As I understand it these calulated "83 l/l" values corresponds to conditions with massive amounts of CO2 (50+% ?) in the feed gas at about ambient temperature and pressure. How well does the system work at depth when the gas only holds fractions of a percent of CO2?

How about the adsorption kinetics? Is it fast enough to cope with the increasing mass flow and (hopefully) decreasing CO2 fraction at depth?

Also since the total pressure and the workload varies during a dive could we expect dramatic differences in CO2 adsorption capacities during different phases of the dive?

Is there any heat of adsorption or will the scrubber temp only be a function of the exhaled gas and water temp? How much does this influence the capacity?

Given that we exhale moist gas, how well will the adsorption scrubber cope with this? Does the moisture create a film that significantly alters the surface area and adsorption kinetics and capacity? Of course some sort of hydrofobic membrane could perhaps fix such issues.

How about the WOB (Work Of Breathing) of these materials?

Also what would this material cost and what sort of gear would it take to regenerate (vaccum pump, oven?)

So lots of questions...

My guess is that we will eventually see this and related stuff in rebreathers. Perhaps even cool stuff such as "self filling" O2-sources that selectively extract oxygen from the air between dives and then with some encouragement releases it at our convinience during the dive.